NI_Skarns and Contact Aureoles - Reservoirs of metals and heat (SCAR)

Lead Research Organisation: British Geological Survey
Department Name: Minerals & Waste

Abstract

Transition to a low-carbon future requires technologies based on critical metals and sustainable energy production. Geological systems associated with convergent plate boundaries host considerable amounts of mineral resources and significant geothermal energy potential, both controlled by super-hot (>350C) fluids at depth. The development of supercritical geothermal resources is a global challenge that cannot be solved by a single country alone. The SCAR project will bring together leading research groups in metallogenesis and mineral extraction (British Geological Survey and Mexican Gold Corp) and geothermal systems (Autonomous University of Mexico, University of Michoacana and the Italian National Research Council) to evaluate the inter-dependency between super-hot fluids, mobilisation and distribution of critical metals (Te, Bi and In) and heat flow. We propose a collaboration focussed on the Tatatila-Las Minas Cu-Au deposit (in the Trans Mexican Volcanic Belt) which can provide data essential for modelling the potential and efficiency of simultaneous extraction of metals and energy from super-hot geothermal systems. A UK-Mexico collaboration aligns well with UK Government initiatives of setting up new partnerships to boost sustainable economies. Dr Alicja Lacinska, lead proposer of SCAR, is a New Investigator whose ambition is to forge new international partnerships to deliver high quality crosscutting science in anticipation of future large-scale metallogenic-geothermal initiatives worldwide.

Publications

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Description The transition to a low-carbon future relies on the development of new technologies and sustainable energy production. Advanced technology requires a wide range of critical metals. These are raw materials which are critical to the economy but at high supply risk and for which there are no viable substitutes with current technologies. Most critical metals co-occur with other metals, for example, tellurium, an essential component of photovoltaic cells in solar panels, is recovered as a primary ore from only two districts in the world (China and Sweden), whilst the majority of it is produced as a by-product of the mining of porphyry copper deposits1.
The utilisation of indigenous high temperature geothermal resources will be crucial to the sustainable development of many countries. Maximising the power output from these resources will be necessary, especially given the high up-front cost linked to drilling boreholes. Future geothermal energy production will thus likely tap deep reservoirs with 'super-hot' temperatures (>350°C). These superhot geothermal systems (SHGS) offer the tantalizing prospect of a ten times increase in power output per borehole, but present significant technical challenges.
The concurrence of mineral resources and geothermal energy potential at plate boundaries (such as along the 'Ring of Fire') makes building a deep understanding of the critical factors that control these systems of global importance.
A fundamental control on the formation of mineral deposits associated with geothermal fields is the flow of super-hot (>350°C) supercritical fluids at great depth - at the same time, depositing strategically important elements and carrying the heat to power overlying geothermal systems. In turn, this fluid movement is controlled by lithologies with good permeability, (i.e. faults and fractures) and sufficient reactivity to cause changes in fluid chemistry that drive mineral formation. Carbonate rocks (e.g. limestone, dolomite, marble) have such properties, and when very hot, vapour-rich fluids given off by cooling granite magma chambers encounter them, it leads to the formation of metamorphic rocks called 'skarns'. Whilst skarns are typically dominated by minerals rich in calcium, magnesium and silicon, they commonly host metallic mineralisation (copper, lead, gold, zinc, bismuth, tellurium, tin, tungsten etc.) of economic significance.
The Tatatila-Las Minas deposit (belonging to the Trans-Mexican Volcanic Belt) that is an exhumed Cu-Au skarn deposit has been mined since historical times, and is now under renewed exploration interest. It represents the deep roots of a palaeo-geothermal system, and as such is considered an analogue of the deep plumbing system of SHGS. It offers a natural laboratory to study the mineralogical and geochemical processes that governed the evolution of the metallogenetic-geothermal system. Petrographic investigation of selected samples from the Las Minas project suggests that the composition and textures of the deep fracture network is highly heterogeneous, and largely depends on the type of the host, i.e. calcic versus magnesian skarn and, the geochemistry of the migrating fluid. The fractures are thus, dominated by calcium and/or magnesium carbonate and silicate minerals that range from unhydrous olivine or pyroxene and/or garnet to their hydrated counterparts, including serpentine minerals and talc. These mineral assemblages collectively control the bulk fluid flow in the system and thus, the distribution and the likely paragenetic associations of the metallic mineralisation. The current state of fractures is a result of multi-step fluid-rock interaction processes, with the early high temperature paragenetic assemblages over-printed by low temperature retrograde hydrous processes. Metallic mineralisation is commonly associated with the latter. Studying the intimate geochemical inter-dependency between the carbonates, the silicates and metals and, the interplay between mineral species and texture of a metasomatic assemblage within, and adjacent to, fractures will provide a unique insight into the critical processes governing the evolution of the system as a potential for future integrated metals-bearing SHGS.


1. R. J. Goldfarb, Berger, B.R., George, M.W., and Seal, R.R., II, 2017, DOI: https://doi.org/ 10.3133/pp1802R.
Exploitation Route The outcomes of this work are of importance to a range of stakeholders interested in the exploitation of super-hot geothermal resources, including both academia and industry. We highlight the importance of a full-system fracture understanding to the assessment of fluid pathways and the efficiency of energy and metal recovery.
Sectors Creative Economy,Energy,Environment
URL https://www.researchgate.net/publication/368921992_Fracture_mineralogy_in_Las_Minas_Mexico_TMVB_implications_for_combined_metal_and_heat_extraction_from_super-hot_geothermal_systems
 
Title Microanalysis of metasomatic veins 
Description This dataset contains Scanning Electron Microscopy images and numerical data acquired to understand the potential of skarns and contact aureoles as a reservoirs of metals and heat. 
Type Of Material Data analysis technique 
Year Produced 2022 
Provided To Others? No  
Impact This work is ongoing, it was impacted by Covid. 
 
Description ENEL green energy 
Organisation Enel SpA
Country Italy 
Sector Private 
PI Contribution The SCAR project team was introduced to the ENEL green energy, operating the Larderello Geothermal power plant during our visit to Italy in OCt 2021. This is a new link, that will hopefully lead to new partnership and collaboration
Collaborator Contribution The ENEL staff have led site introduction in Larderello, as in-kind support
Impact Outcome - new network, with representative of ENEL to visit SCAR project in UK, at the end of March, during another networking, partnership building event organised by SCAR project, Cornwall Geothermal
Start Year 2021
 
Description Italian National Research Council 
Organisation Italian National Research Council
Department Institute of Geosciences and Georesources
Country Italy 
Sector Charity/Non Profit 
PI Contribution One of the main objectives of the SCAR project is to establish strong partnerships, and to this extend my research team organised a partnership building visit to Italy in October 2021. This visit was between 3 BGS staff and 2 Italian Research Council staff. The objective of the visit was to exchange knowledge from the Italian experts to the UK researchers on the geothermal system in Larderello, Italy.
Collaborator Contribution The Italian Research Council partners have organised a 3 day networking trip in Italy, and provided scientific and logistical support.
Impact 1. Joint field trip, networking and knowledge exchange. 2. Ongoing data acquisition 3. A peer -review paper in preparation
Start Year 2021